JANIS SHARP: It was an incredibly brave decision. To stand up to another nation as strong and powerful as America is rare and she had the guts to do it.

RACHAEL BROWN: This may the first and last time the Home Secretary blocks an extradition on human rights grounds.

A review she commissioned recommended those decisions be left to judges.

But her compassion is raising ire and eyebrows in the US.

Extradition expert Douglas McNabb says the US Attorney's office is going to be livid.

DOUGLAS MCNABB: They may request Interpol, out of Lyon, to issue a red notice.

And that red notice will be sent to 190 countries, putting them on notice that there's an outstanding arrest warrant out in the US.

So that if Mr McKinnon were to leave the UK and travel to country X, the red notice is going to be- will pop up and he'll be arrested and placed in extradition proceedings between country X and the US.

RACHAEL BROWN: US lawyer David Rivkin was a White House Counsel for presidents Reagan and Bush.

He says the Home Secretary's decision is laughable and could set a dangerous precedent.

DAVID RIVKIN: Under that argument, why do you even arrest anybody?

A person would say "If you arrest me and put me in a British prison, I'm going to kill myself."

RACHAEL BROWN: He says the extradition treaty has become a political football.

DAVID RIVKIN: We live in a world where individuals in one country can carry out crimes against another country.

We're supposed to work on this in a co-operative fashion, we're supposed to respect each other's judicial system.

RACHAEL BROWN: And the treaty could get even more complicated.

Theresa May again.

THERESA MAY: I have decided to introduce a forum bar.

MPs: Hear, hear.

THERESA MAY: This will mean that where prosecution is possible in both the UK and in another state, the British courts will be able to bar prosecution overseas if they believe it is in the interests of justice to do so.

SHAMI CHAKRABARTI: It's a future where we will see discretion to consider where alleged activity took place, and where people who are accused of doing things in Great Britain get the opportunity to be tried in Great Britain.

RACHAEL BROWN: It's the same argument that was tested in the recent case of terrorism suspects Babar Ahmad and Talha Ahsan.

They were extradited to the US earlier this month, accused of running extremist websites.